A piezoelectric element has been used as a material of a transducer in an ultrasonic probe in the related art. In recent years, a CMUT chip formed by a semiconductor device has been adopted as a transducer of an ultrasonic probe.
In the case of the CMUT chip, acoustic-electric conversion efficiency of the transducer is low compared with a piezoelectric element. For this reason, the CMUT chip has a technical problem in that it is easier to cause multiple reflections than the piezoelectric element.
The multiple reflections are a phenomenon in which reflection of ultrasonic waves on a reflective surface is repeated with the boundary of tissue or the like in an object as the reflective surface. This means a phenomenon in which artifacts of a structure, which is not present in the measurement range of an ultrasonic probe, appear.
Therefore, in order to solve the problem of multiple reflections of a transducer having a CMUT chip, PTL 1 discloses a technique of reducing the multiple reflections of a transducer per channel by meeting both the following first and second conditions.
Firstly, the first condition is to satisfy the condition of 6.5/fc<αd where the absorption coefficient of the acoustic lens is α [dB/mm/MHz], the maximum thickness of the acoustic lens is d [mm], and the center frequency of the transducer is fc [MHz].
Then, the second condition is to satisfy the condition L<1/((3πfc) 2×C) where the inductance value of the transducer per channel is L [H], the capacitance of the transducer per channel is C [pF], and the center frequency of the transducer is fc [MHz].